It is important when choosing any form of silicone sponge to understand the difference between open and closed cell. Confusing the two could lead to failure of a seal or gasket in application.

Open Cell Sponge

Open cell basically means that each cell, or if you like bubble, is openly connected to the next cell. These cells are not complete closures therefore water, moisture and dust can very readily make their way into the cell structure.

A good example of an open cell sponge is the type of sponge that is used to wash a car or wash the dishes at home. If you place the sponge in a bucket of water, you see the sponge soaking up lots of water which is then squeezed out again onto the car. The water is allowed to pass through each cell and therefore gets absorbed and held within the sponge.

Closed Cell Sponge

Closed cell sponge has a much different cell structure to open cell. Each cell in a closed cell silicone sponge is a complete closed sphere trapping air within each cell. Unlike open cell, water, moisture and dust cannot readily enter the cell structure due to the lack of connectivity between the cells. Closed cell sponge is great for sealing when water and dust need to be kept out of an application as it has very low water absorption. Our silicone sponge can achieve IP65 and IP66 ratings for sealing performance.

silicone sponge sheets

What is Water Absorption?

At Silicone Engineering we produce closed cell silicone sponge. This is a big selling point as many applications require protection from water and dust ingress.

We’ll use the example of what would happen if an open cell sponge was used in an airplane assembly; If the sponge seal absorbed moisture on the ground, once in flight at 32,000 ft the moisture would then freeze causing the assembly to expand, crack and fail, potentially causing a disaster.

Due to very low water absorption in closed cell sponges this would not happen and is why they are used as seals and gaskets in the Aerospace industry.

plane impeller
Picture of a propeller engine (airplane) against sky


Closed cell sponges also tend to be a lot firmer because when you press the sponge, as well as compressing the rubber you are also compressing the air inside the cells. With open cell sponges this air can escape when compressed therefore the only resistance is from the rubber itself.

So when choosing silicone sponge for a certain application, make sure you understand the difference between open and closed cell.

Discover more about Silicone Engineering’s closed cell sponge grades, both sponge sheeting and sponge extrusions


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